Concrete-filled Steel Columns Research Articles

A study on self-curing self-compacting concrete filled steel columns subjected to axial compression

For vehicle parking areas, in multi-storey buildings and bridge piers, composite tubular columns have been considered as a better solution. The cold-formed steel and concrete combination is notable, because of the benefits of inherent material properties of both the materials. Concrete filled tubular (CFT) columns is in-filled with concrete having single tubes or concentric double tubes leaving the core as hollow. Moreover, for the design of such composite columns a specific design code is yet to be released in India. Henceforth, this experimental research intends to study the structural behaviour of CFT columns, consisting steel tube in terms of load- deflection graph, ultimate load carrying capacity, confinement of concrete and ductility. The structural use of a unique Self-Curing and Self-Compacting Concrete (SCSCC) using 10% granite saw dust waste and 25% fly ash as partial replacement to cement was confirmed. The experimental results are compared with computer modelling analysis done using ABAQUS for a better understanding of the column specimen's behaviour. Based on experimental studies percentage of super plasticizer and Super Absorbent Polymer (SAP) is determined as 1.3% & 0.3% respectively. The variation between experimental and analytical results is minimum and is due to minor material defects in steel sections. In this present experimental study three different cross sections namely: (i) cylindrical (ii) rectangular and (iii) square cross sections with 500 mm length and 2 mm thickness was used. Secondly a parametric study was conducted for 3 different lengths and 3 thickness which also showed that the performance of square cross sections was effective irrespective of the lengths. The load carrying capability of columns with increased steel section thickness is seen to be greater for the same length of column. When compared to cylindrical sections, rectangular and square sections show a significant reduction in load carrying capability as the thickness of the steel section is reduced. These changes in load carrying capacity are mainly due to the shape factor. The main advantage of the CFST column is that it has a better ultimate strength than a regular column due to the concrete confinement. This increased strength due to confinement is higher in cylindrical specimens.

Optimized design of concrete-filled steel columns

Abstract The objective of this paper is to present the formulation of the optimization problem and its application to the design of concrete-filled composite columns with and without reinforcement steel bars, according to recommendations from NBR 8800:2008, NBR 16239:2013 and EN 1994-1-1:2004. A comparative analysis between the aforementioned standards is performed for various geometries considering cost, efficiency and materials in order to verify which parameters influence the solution of the composite column that satisfies the proposed problems. The solution of the optimization problem is obtained by using the genetic algorithm method featured in MATLAB’s guide toolbox. For the examples analyzed, results show that concretes with compressive strength greater than 50MPa directly influence the solution of the problem regarding cost and resistance to normal forces.

Short columns composed of concrete-filled steel tubes in a fire situation – Numerical model and the “air-gap” effect

Abstract The increase in temperature reduces the strength of steel and concrete, in such a way that it is essential to verify concrete-filled steel tube columns in fire situations. Numerical simulations, with lower costs than laboratory tests, have great importance in checking resistance and defining simplified methods for design practice. However, peculiarities of the thermal and mechanical behavior of heated confined concrete and the air-gap effect (a phenomenon inherent to concrete-filled steel columns) must still be better understood. Therefore, this study presents the development of a numerical model performed in the ABAQUS software (Dassault Systemes SIMULIA Corp., 2014) for the thermomechanical analysis of short columns composed of circular and square concrete-filled steel tubes considering the air-gap effect. The air-gap phenomenon is presented and analyzed according to possibilities of implementation to the numerical model and, finally, the proposed numerical model is validated with experimental results presented in the literature. According to the study results, the numerical model can be used to define and adjust simplified methods for verification of composite columns in fire situation. The importance of considering the air-gap effect in numerical modeling was confirmed, taking into account that disregarding its effect may result in overestimated responses of the steel tube resistance in fire situations. Moreover, it was suggested thermomechanical joint analysis and the use of the explicit solver as a strategy to minimize processing time.

Lateral Impact Response of Elliptical Hollow and Partially Concrete-Filled Cold-Formed Steel Columns Under Static Axial Compression Load

In recent years, the use of partially concrete-filled steel tubular (PCFST) columns has been considered due to their cost-effectiveness and reduction of structural weight in bridge piers and building columns. One of the critical discussions about these columns is their impact resistance. In this article, the dynamic response of hollow and PCFST columns with elliptical cross-section under simultaneous loading of static axial compressive load and lateral impact load is presented using finite element modeling in ABAQUS software (FEA). To ensure the accuracy of the numerical modeling, the analysis results are compared with the results of previous works. The effects of different parameters such as impact velocity, the height of the impact location, the impact direction, the impact block mass, the size and shape of the impact block are investigated in this paper. The results of the numerical analysis showed that the partially filled specimens had better performance than the hollow specimens. The changes in impact direction and impact block mass parameters have a significant effect on the failure of the columns, especially when they are under high impact velocity. Changing the impact velocity significantly affects the impact resistance of specimens. However, the size and shape of the impact block did not have a significant effect on the displacement of the column against the impact loading.

Impact behavior of concrete-filled steel tube with cruciform reinforcing steel under lateral impact load

The objectives of this research are to investigate the behavior of cruciform steel-reinforced concrete-filled steel columns under impact load through experimental and numerical studies. The effects of impact velocity/height, axial pressure, thickness of steel tube and boundary conditions on the impact resistance of composite columns are studied through the tests of 16 specimens. The detailed progressive responses were recorded, including deformation mode, impact force-time history, deflection-time history and axial force-time history. Based on the test results, the impact resistances of steel-reinforced concrete-filled steel tubular columns and concrete-filled square steel tubular (CFST) columns are compared. In addition, FE models of the composite column are established using ABAQUS and validated based on experimental data. The strain rate effect of steel and concrete is considered in the model. The results show that the outer square steel tube effectively protects the internal steel-reinforced concrete. In the impact energy range of 17.02–51.08 kJ, the specimens only suffer minor bending deformation, which shows their excellent impact resistance. The ultimate plastic strain energy of square steel tube (EPT), cruciform steel section (EPS) and concrete (EPC) accounts for 56.4%, 18.2% and 25.4% of the total energy dissipation, which suggests that the steel tube (EPT) is the main energy dissipation mechanism of concrete-filled square steel tube columns.

Impact of Temperature Rise on the Seismic Performance of Concrete-Filled Double Skin Steel Columns with Prismatic Geometry

Abstract This paper studies the impact of temperature rise on the performance of Concrete-Filled Double Skin Tubular Steel Columns with prismatic geometry. In doing so, several columns whose interior cores were square, diamond, and circularly shaped and whose exterior cores were prismatic with a square cross-sectional area that increases with the slope of 2.1 degrees from top to the bottom, were constructed and exposed to the temperatures of 25°C, 250°C, 500°C, and 700°C. Afterward, all column specimens were subjected to cyclic loads adopted from the Applied Technology Council (ATC)-24 loading protocol, which proceeded until the specimens failed to further carry loads. The results indicate that although the failure modes of the columns with an interior core of a square or diamond shape are similar to each other, the columns whose interior cores were circularly shaped experienced more intensive damages compared to the others. The base of the columns was fractured diagonally with a degree of 45 by the temperature of 500°C, but at 700°C, the damages have occurred horizontally at the height of 10 cm from the column base. Moreover, the initial stiffness and ductility ratio of the columns with a diamond-shaped interior core was approximately two times greater than the other columns.

Response and modeling of axially-loaded concrete-filled steel columns with recycled coarse and fine aggregate

Recycled aggregate concrete-filled steel tube (RACFST) could be a practical structural application of recycled aggregate concrete (RAC) with fine recycled aggregate (FRA). Despite its great potential, limited attention has been devoted to the compressive response of RACFST with FRA. This study investigates the effects of FRA on the structural response of RACFST with different coarse recycled aggregate (CRA) replacement ratios (rC), and how FRA influences the confinement effect of RACFST. Fifty-four RACFST specimens were tested to failure with different FRA and CRA replacement ratios (rF and rC), concrete strengths (fcm) and effective steel ratios (α). Experimental results show that FRA and CRA have a significant compounding effect (i.e., FRA effect is different at varying rC) on the strain at the maximum load (ε0) of RACFST. Unlike CRA which has an insignificant influence on the confinement effect, the use of FRA significantly reduces the confinement of RACFST. The test results were used to modify the existing mathematical expressions for normal concrete-filled steel tube (CFST) to predict the stress-strain relationships for RACFST. The predicted results matches well with the available test data.

Analytical models for predicting the load-bearing strength of beam-to-column joints in a composite steel frame

Two analytical models are developed to predict the load-bearing capacity of a beam-to-column joint inside a slim-floor composite frame. The load inside the joint is transferred mainly by a steel console welded to a concrete-filled steel column. Because of the asymmetric nature of plastic collapse mechanism of the steel console, a two-parameter model is developed in two mechanisms: a mechanism excluding the axial force at hinge lines, and an intuitive mechanism including the influence of arising axial force. The models are verified by numerical results and used further for parametric studies. The results indicate that both models predict the limit load of the joint well. The studies also show that the model excluding the normal force is simple to use but can be a bit conservative, whereas the model including the normal force better predicts the load-bearing capacity of the joint, particularly if larger indentation is allowed. Based on the parametric studies, a general equation is then proposed. Compared to the method provided in design code as EN 1993-1-8, the proposed equation predicts the higher load-bearing capacity; thus leading to a more economical design in practice.

Presentation of Critical Buckling Load Correction Factor of AISC Code on L-Shaped Composite Columns by Numerical and Experimental Analysis

Concrete-filled steel tubular (CFT) columns have been widely used as structural members in buildings and bridges in recent years, because of their properties, such as high strength and stiffness, good ductility, and convenience for construction. In CFT columns, the bearing capacity of columns is inversely related to buckling, therefore, buckling is of particular importance at these sections, the AISC Code uses effective bending rigidity (EIeffective) to calculate the critical buckling load in concrete filled steel columns, to apply the effect of reducing concrete confinement, the AISC code provides a maximum value of 0.9 of the reduced concrete confinement coefficient for the equation. Effective bending rigidity (EIeffective), this relationship is provided in AISC code for circular and square sections, therefore, the effect of the column shape geometry on the core concrete confinement is very influential and changes the effective bending rigidity (EIeffective) of the section. The AISC code does not provide a coefficient to consider the type of cross-sectional geometry in CFT columns, therefore, in this study, three groups experimental, numerical (FEM) and theoretical were used to provide critical buckling load correction, finally, it was concluded that the critical buckling load for the cross-section (L) shape due to the lower confinement of the concrete core is 20.07% lower than the AISC code equation, also with a 67% increase in slenderness ratio, the critical buckling load decreased by 14.52%.

Numerical Modeling of Recycled and Normal Aggregate CFRP-Strengthened Concrete-Filled Steel Columns Subjected to Lateral Impact

Abstract This paper presents 3D nonlinear finite element analyses on concrete-filled steel-tube (CFST) columns subjected to lateral impact loading by considering concrete type, projectile configura...

Behaviour of through plate connections to concrete-filled stainless steel columns

Bond between stainless steel and concrete is not reliable for load transfer in concrete-filled stainless steel tubular (CFSST) columns. This paper proposes the use of a full-through plate for connecting the primary beam to a stainless steel composite column, whereas half-through plates are used to connect other secondary beams. In fabricating such connections, welding of through plates inside a steel tube can be avoided. This paper presents an experimental investigation of the properties of such through plate connections, and the test results are compared with those of blind-bolted endplate connections tested in our earlier research. Meanwhile, finite element models are developed with an aim to compare the behaviour of through plate connections with that of fin plate connections in terms of initial stiffness, flexural resistance and rotation capacity. It is found that the through plate connection with slab exhibits semi-rigid behaviour. Its initial stiffness and flexural resistance are lower than those of the blind-bolted endplate connection, but the rotation capacity is higher. Both the through plate and fin plate connections have similar flexural resistance, but the former has much higher initial stiffness. This study confirms that it is feasible to have a combined use of full-through and half-through plates for connecting beams to CFSST columns. This arrangement might also be suitable for normal composite columns if there is not sufficient bond to enable load transfer.

FRP-confined steel-reinforced recycled aggregate concrete columns: Concept and behaviour under axial compression

This study introduces the compressive behavior of FRP-confined steel-reinforced concrete (FCSRC) columns using recycled aggregate concrete (RAC). The performance of RAC is generally inferior to the natural aggregate concrete (NAC). In terms of optimized use of different materials, FCSRC column using RAC is a promising hybrid column because of the following merits: 1) using RAC in FCSRC columns is deemed to overcome its weakness since RAC is double confined by the encased steel column and FRP; 2) local/global buckling of the encased steel section can be allayed or suppressed; 3) both concrete and steel section can be protected by FRP against harsh environmental attack. In this study, FCSRC columns with RAC under concentric compression were tested to explore the effects of replacement ratio of recycled coarse aggregates (RCAs) and FRP confining stiffness. It has been revealed that the FCSRC columns with RAC had similar compressive behavior as the FCSRC columns with NAC although the use of RAC slightly decreased the load-carrying capacity. Favorable interactions existed among FRP, concrete and steel, but full composite effect was not achieved by combining the concrete-filled FRP tube (CFFT) and steel column due to the occurrence of local buckling in the encased steel column.

Research on Construction Method of Concrete Filled Steel Column

As a new type composite structure, concrete fill steel column has a good performance and is widely used in super high rise building. However, concrete pouring and quality control are challenges all the time. Combining with actual engineering projects, this article analyzes key and difficult points existing in concrete filled steel column construction and explores construction in different aspects like selection of construction method, simulated column construction and main construction method introduction. Hoping this article has some help for the similar projects later.

Compressive behaviour of concrete-filled carbon fiber-reinforced polymer steel composite tube columns made of high performance concrete

The confinement of concrete-filled steel columns (CFT) with carbon fiber-reinforced polymer (CFRP) has been extensively studied in recent decades due to their significant applications for the strengthening purposes or construction of composite structures. A CFT column consists of a steel tube and inner-filled concrete, where the steel tube is used as a form and confinement of the concrete, with the concrete being the core that prevents buckling of the tube. Due to the development of concrete technology, high performance concrete (HPC) is increasingly used as the internal material of CFT. However, CFT columns are susceptible to local buckling and constant confining stress after yielding of the steel tube. This is why concrete-filled carbon fiber-reinforced polymer steel composite tubes (CFCT) have been considered. The key parameter, which determines load-carrying capacity, and axial and transverse deformation is the number of CFRP layers. The test results showed that local buckling of the steel tube can be effectively eliminated and that the compressive strength of CFCT is enhanced by the external confinement. It has been shown that the stress-strain characteristic depends on confinement pressure. This paper also discusses damage patterns and presents analysis of limit load capacity based on both laboratory experiments and numerical calculations.

Fire Resistance of Axially and Rotationally Restrained Concrete-Filled Double-Skin and Double-Tube Hollow Steel Columns

AbstractThe use of concrete-filled hollow steel columns is increasing in construction. These columns with a high load-bearing capacity allow the use of smaller cross sections. However, the use of s...

A review on concrete-filled steel hollow column subjected to fire and cyclic loadings

Concrete-filled hollow steel column (CFHS) column is a composite column that comprised of concrete core filled into hollow steel section. The composite action between the hollow steel sections and concrete core give CFHS better performance over conventional reinforced concrete and steel column. Numbers of studies had been done on the performances of CFHS with different types of the concrete core subjected to various loadings. The concrete filling materials used by previous researchers including plain concrete, reinforced concrete, and other modified concrete such as concrete containing fly ash, recycled aggregate and rubber particles. This paper presents the performances of CFHS with different type of concrete filling materials subjected to fire and cyclic loadings. A comparison between different concrete filling materials that have been used to fill hollow steel column that were used by previous researchers are presented. Research gap and recommendations are also proposed for further study.

Numerical study on axially loaded ultra-high strength concrete-filled dual steel columns

This paper presents a numerical investigation on the mechanical performance of concrete-filled dual steel tubular columns of circular section subjected to concentric axial load. A three-dimensional numerical model is developed and validated against a series of experimental tests. A good agreement is obtained between the experimental and numerical results, both in the peak load value and in the ascending and descending branches of the load-displacement curves. By means of the numerical model, a parametric study is carried out to investigate the influence of the main parameters that determine the axial capacity of double-tube columns, such as the member slenderness, inner and outer steel tube thicknesses and the concrete grade – of both the outer concrete ring and inner core –, including ultra-high strength concrete. A total number of 163 numerical simulations are carried out, by combining the different parameters. Specific indexes are defined (Strength Index, Concrete-Steel Contribution Ratio, Inner Concrete Contribution Ratio) to help rating the relative mechanical performance of dual steel tubular columns as compared to conventional concrete-filled steel tubular columns, and practical design recommendations are subsequently given.

Shear transfer mechanism in connections involving concrete filled steel columns under shear forces

This paper reports the experimental results of three through bolt beam-column connections under pure shear forces using modified push-out tests. The investigated specimens include extended end-plates and six through-bolts connecting square concrete-filled steel tubular column (S-CFST) to steel beams. The main goal of this study is to investigate if and how the mechanical shear connectors, such as steel angles and stud bolts, contribute to the shear transfer mechanisms in the steel-concrete interface of the composite column. The contribution of shear studs and steel angles to improve the shear resistance of steel-concrete interface in through-bolt connections was investigated using tests. The results showed that their contribution is not significant when the beam-column connection is included in the push-out tests. The specimens failed by pure shear of the long bolts, and the ultimate load can be predicted using the shear resistance of the bolts under shear forces. The predicted values of load allowed obtaining a good agreement with the tests results.

Nonlinear Numerical Analyses of a Fabricated Connection of Concrete-Filled Steel Column to Steel Beam Under Low-Reversed Cyclic Loading

Introduction: Based on FEM program ABAQUS, three-dimensional numerical models of a fabricated connection of concrete-filled steel column to steel beam under low-reversed cyclic loading were established by considering both nonlinearity of material and geometry. Effects of stiffen ring plate, axial compression ratio and backing plate on the hysteresis curves, skeleton curves, ductility coefficient and energy dissipation coefficient were analyzed respectively. Methods: Furthermore, parametric analyses with comparison were also conducted to discuss the mechanical characteristics and damage mechanism of the fabricated connection. Results: The results show that there are clear stress concentrations near the area of bolt holes in beam flange. The increase in width of ring plate and the shape change of ring plate from square to circle can both improve the ductility and the characteristics of hysteretic behavior. Besides, the backing plates have positive effects on the hysteretic characteristics, ductility and energy dissipation of the CFST column connections. Oppositely, the increase in axial compression ratio contributes negatively to both the bearing capacity and deformation performance of the connection specimens. Conclucion: It can be concluded that the fabricated connection displays good working performance relating to hysteretic characteristics, energy dissipation and ductility, which can be hopefully applied and provide reference to engineering practice.

Behavior of a concrete filled steel box column with considering detachment under seismic load

Various numerical studies have been conducted on the dynamic behavior of concrete-filled steel columns. However, the detachment caused by the tensile stress between the steel plates and the concrete is rarely considered. This paper describes the results of dynamic numerical analysis conducted on a concrete-filled steel box column used as a pier of a motorway viaduct under seismic load, with detachment considered as a contact problem. The results obtained indicate that detachment causes large residual displacement and reduces the peak load of the column. Further, the influence of the detachment on column behavior is shown to depend on the depth of the concrete.